There are three main indications associated with draw-out breakers that every test technician should know. Photo: EMSCO.
Draw out circuit breakers are equipped with three important flags that indicate the operating state of an electrical circuit. Thorough knowledge of these indications and their associated assembly is critical in order to correctly operate and maintain circuit breakers.
The important controls and indicators are grouped on the front of the breaker by function. Each flag represents a separate mechanism that controls the installation, connection, or removal of the circuit breaker.
There are three main indications associated with draw-out breakers that every qualified person must know:
Unlike bolt-in circuit breakers, draw-out breakers are designed to mount on extension rails and are equipped with racking mechanisms for easy interchangeability. These circuit breakers have 4 racking positions:
Draw-out breakers are designed to mount on extension rails and are equipped with racking mechanisms for easy interchangeability. Photo: EATON
Withdrawn - Circuit breaker is outside of the compartment or switchgear cubicle on extension rails. No electrical connections are made at the primary or secondary contacts. The racking mechanism is not engaged. Also called the “Remove” or “Inspection” position.
Disconnected - Typical storage position, the circuit breaker is fully inserted behind the compartment front door. Only the ground connection is made; primary and secondary connections are not made. The racking mechanism is engaged and the circuit breaker is ready to be racked in. When racking out circuit breakers, the operating springs should automatically release, if charged.
Test - Position used for breaker and trip unit testing. Circuit breaker is partially racked into the compartment. Only the secondary and ground connections are made; primary connections are not made. The circuit breaker might charge electrically when placed in this position, if discharged and equipped with an electric operator.
Connected - Circuit breaker is fully racked into the compartment and is ready for operation. Primary, secondary, and ground connections are made.
Note: Racking mechanisms are sometimes referred to as “levering” mechanisms. Racking a circuit breaker, whether in or out, presents the greatest arc flash risk to personnel.
Power circuit breakers are equipped with a two-step stored energy mechanism to facilitate the opening or closing of the main contacts by stretching or compressing powerful springs.
The two-step stored energy process allows for an open-close-open duty cycle, which is achieved by storing charged energy in a separate closing spring. The spring indicator has two positions:
Charged - Stored energy is present in the closing springs and the circuit breaker is ready to close if required. It is possible to recharge the springs immediately after closing the circuit breaker and before it has been tripped open.
Discharged - Stored energy is NOT present in the closing springs. The closing springs must first be charged before the circuit breaker can be closed. Stored energy is still present in the opening springs if the breaker is closed.
On a manually operated circuit breaker, the closing spring can only be charged manually. For electrically operated circuit breakers, the springs are normally charged through the use of an electrical operator but can be charged manually as well.
The important controls and indicators are grouped on the front of the breaker by function. Photo: EMSCO.
Each circuit breaker primary moving contact assembly is comprised of multiple individual copper contact fingers connected to the load conductor through a pivoted or flexible connection. The number of fingers used depends upon the breaker’s continuous and short-circuit current ratings.
There are three positions for the primary contacts:
Open - Main contacts are not connected, preventing power from flowing through the circuit.
Closed - Main contacts are connected, allowing power to flow through the circuit.
Tripped - Main contacts have been parted by the circuit breaker protective device. The breaker must be properly reset before reclosing otherwise it will trip free.